1. Field of the Invention
The present invention relates to an evaporated fuel treatment apparatus for treating evaporated fuel.
2. Description of the Related Art
For example, on a vehicle provided with an internal combustion engine, when a fuel tank is filled with liquid fuel, the occupied volume of the liquid fuel reserved in the inner space of the fuel tank increases. As a result, the occupied volume of the gas phase region in the inner space relatively decreases so that the pressure of the gas phase region (hereinafter, referred to as ‘tank internal pressure’) becomes higher than the atmospheric pressure. Consequently, the evaporated fuel of the gas phase region remaining in the fuel tank urges to get out into the atmosphere. If the evaporated fuel is released out into the atmosphere, the atmosphere (global environment) comes to be contaminated.
In this situation, in order to prevent contamination of the atmosphere (global environment) caused by releasing evaporated fuel out into the atmosphere, a conventional evaporated fuel treatment apparatus is provided with a canister having an absorbing member at a communication passage between a fuel tank and the atmosphere to temporarily absorb the evaporation material, and the evaporated fuel is thereby absorbed by the absorbing member of the canister so that the tank internal pressure is prevented from increasing.
For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2006-77595 (Paragraphs 0028-0030)) discloses an evaporated fuel treatment apparatus that includes a fuel tank, a canister, a charge communication passage for communication and connection between the fuel tank and the canister, an air communication passage for communication and connection between the canister and the atmosphere, a vent shut valve for opening and closing the air communication passage, a purge communication passage for communication and connection between the canister and an internal combustion engine, and a purge control valve for opening and closing the purge communication passage. The vent shut valve is open during fuel feeding or purge execution. The purge control valve is open during purge execution.
On the evaporated fuel treatment apparatus disclosed by Patent Document 1, after an internal combustion engine is stopped, selectively used are a first determination method based on a parameter corresponding to the secondary differential value of the internal pressure of the fuel tank and a second determination method based on a stagnation time of the internal pressure of the fuel tank, and performed is leak diagnosis of the evaporated fuel tightly-sealed system including the fuel tank. Concretely, if the generation amount of the evaporated fuel in the fuel tank is comparatively large, a diagnosis result by the first determination method is selected while, if the generation amount of the evaporated fuel is comparatively small, a diagnosis result by the second determination method is selected.
The evaporated fuel treatment apparatus according to Patent Document 1 enables accurate leak diagnosis of the evaporated fuel treatment apparatus with a comparatively simple configuration during when an internal combustion engine is stopped.